Regular Expressions in .NET

1. Regular Expressions in .NET BY Sandeep Kumar Gampa.

2. Contents. • What is Regular Expression? • Regex in .NET • Regex Language Elements • Examples • Regular Expression API • How to Test regex in .NET • Conclusion

3. What is Regular Expression? • A regular expression (regex or regexp for short) is a special text string for describing a search pattern. • A regular expression is a set of pattern matching rules encoded in a string according to certain syntax rules. • The syntax (language format) described is compliant with extended regular expressions (EREs) defined in IEEE POSIX 1003.2 • Sample Example for Email Id ^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$

4. Regex in .NET • Validation in ASP.NET , We use the RegularExpressionValidator control to validate that input Fields. such as Name, Email Id, Urls, Date • Also when certain patterns need to be replaced by a String. Like Regex.Replace(intput, @“Pattern1", “Pattern2”} • To reformatting an input string by re-arranging the order and placement of the elements within the input string Example: If a date is in DD-MM-YYYY format and is to be changed into MM-DD-YYYY format.

5. Regex Language Elements • Metacharacters - The constructs within regular expressions that have special meaning are referred to as metacharacters - Characters other than . $ ^ { [ ( | ) ] } * + ? \ match themselves. • Character Classes - Character classes are a mini-language within regular expressions, defined by the enclosing hard braces [ ]. Examples: [a-z A-Z 0-9],

6. Cont… MeataCharacters and their description followed by an example: • ^ Start of a string. ^abc matches are abc, abcdefg, abc123, • $ End of a string. abc$ matches with abc, endsinabc, 123abc • . Any character (except \n newline) • | Alternation. • {...} Explicit quantifier notation. • [...] Explicit set of characters to match. • (...) Logical grouping of part of an expression. • * 0 or more of previous expression. • + 1 or more of previous expression. • ? 0 or 1 of previous expression; also forces minimal matching when an expression might match several strings within a search string. • \ Preceding one of the above, it makes it a literal instead of a special character. Preceding a special matching character, see below.

7. Cont… • \w Matches any word character. equivalent to [a-zA-Z_0-9]. • \W Matches any nonword character. Equivalent to the Unicode categories equivalent to [^a-zA-Z_0-9]. • \s Matches any white-space character. equivalent to [ \f\n\r\t\v]. • \S Matches any non-white-space character. equivalent to [^ \f\n\r\t\v]. • \d Matches any decimal digit. • \D Matches any nondigit.

8. Examples Pattern Description • ^\d{5}$ • ^\d{3}-\d{2}-\d{4}$ • ^[01]?[- .]?(\([2-9]\d{2}\)|[2-9]\d{2})[- .]?\d{3}[- .]?\d{4}$ 5 numeric digits, such as a US ZIP code. Validates the format such as 111-11-1111 (Social Security Number) Validates a U.S. phone number.

9. Regular Expression API • Regular Expression classes found in the System.Text.RegularExpressions namespace. • the main classes we'll want to use are Regex, Match, and MatchCollection. • Regex: Methods and their description IsMatch - Returns true if the regex finds a match in the input string. Match - Returns a Match object if a match is found in the input string. Matches - Returns a MatchCollection object containing any and all matches found in the input string. Replace - Replaces matches in the input string with a given replacement string.

10. Cont… • Capture: Represents the results from a single subexpression capture. Capture represents one substring for a single successful capture • CaptureCollection : Represents a sequence of capture substrings. CaptureCollection returns the set of captures done by a single capturing group • Group: Group represents the results from a single capturing group. A capturing group can capture zero, one, or more strings in a single match because of quantifiers, so Group supplies a collection of Capture objects. • GroupCollection: Represents a collection of captured groups. GroupCollection returns the set of captured groups in a single match.

11. How to Test regex in .NET Simple C# Example: • Regex r = new Regex(pattern,    RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace); Match m = r.Match(inputtext); if(m.Success) { Console.WriteLine(“Matched String “+m.Group()); }else{ Console.WriteLine(“Not Matched “); }

12. Example2 • Example: describes how to use other classes. • Using System.Text.RegularExpressions; • string text = "One fish two fish red fish blue fish"; • string pat = @"(?<1>\w+)\s+(?<2>fish)\s*"; • // Compile the regular expression. • Regex r = new Regex(pat, RegexOptions.IgnoreCase); • // Match the regular expression pattern against a text string • Match m = r.Match(text); • while (m.Success) • { • // Display the first match and its capture set. • System.Console.WriteLine("Match=[" + m + "]"); • CaptureCollection cc = m.Captures; • foreach (Capture c in cc) • { • System.Console.WriteLine("Capture=[" + c + "]"); • }

13. Cont… • // Display Group1 and its capture set. • Group g1 = m.Groups[1]; • System.Console.WriteLine("Group1=[" + g1 + "]"); • foreach (Capture c1 in g1.Captures) • { • System.Console.WriteLine("Capture1=[" + c1 + "]"); • } • // Display Group2 and its capture set. • Group g2 = m.Groups[2]; • System.Console.WriteLine("Group2=["+ g2 + "]"); • foreach (Capture c2 in g2.Captures) • { • System.Console.WriteLine("Capture2=[" + c2 + "]"); • } • // Advance to the next match. • m = m.NextMatch(); • }

14. Conclusion • Regular expressions provide a very powerful way to describe patterns in text, making them an excellent resource for string validation and manipulation. • The .NET Framework provides first-rate support for regular expressions in its System.Text.RegularExpressions namespace and specifically the Regex class found there. References: • http://msdn.microsoft.com/en-us/library/system.text.regularexpressions.groupcollection.aspx • http://www.regular-expressions.info/dotnet.html • http://regexlib.com/CheatSheet.aspx

15. Thank You.